The disclosed invention is directed generally to multiplying digital-to-analog converters (DACs), and is directed more particularly to a two quadrant multiplying DAC.
A multiplying DAC multiplies an analog signal (e.g., a current) by discrete gain factor represented by a digital word to provide an output analog signal. Conventional multiplying DACs perform single quadrant multiplication wherein the input analog signal is unipolar and the output analog signal is also unipolar.
Two quadrant multiplication is commonly achieved with two conventional multiplying DACs, one for each polarity of the input signal. One of the multiplying DACs can be implemented with NPN current switches and the other can be implemented with PNP current switches. Considerations with PNP transistor multiplying DAC implementations, however, include speed and resolution limitations.